1. Field of the Invention
This invention relates to industrial gas turbines in general and more specifically to an improved device for reducing the amount of wear that occurs along mating surfaces of a combustion transition duct end frame due to vibration and tolerance issues of the turbine inlet seal.
2. Description of Related Art
Typical industrial gas turbines include multiple combustors, arranged in an array about the engine. These combustors, also known as can-annular combustors, contain the chemical reaction that occurs between fuel and compressor discharge air. The hot gases produced are directed through a turbine that is coupled to a generator used to generate electricity. A typical combustor includes an outer case, a flow sleeve to regulate the amount of compressor discharge air that is introduced into the combustion chamber, and a combustion liner that contains the actual combustion chamber. Fixed to the outer case is a cover assembly that contains at least one fuel nozzle, which can inject liquid and/or gas fuel into the combustion liner. The fuel and compressor discharge air then mix within the combustion liner and react in the combustion chamber. The hot gases formed within each combustor are introduced into the turbine section through multiple transition ducts. The transition ducts are contoured in shape to mate to both the combustor on the forward end and the turbine on the aft end. Given the quantity of individual combustion components, there are a number of interfaces between these components where interaction occurs and depending on the component material and operating conditions significant wear between the mating components can cause premature replacement.
One such area in particular that can suffer from excessive wear is the aft end of the transition duct within the end frame. Wear within the aft end frame is due to its interaction with the floating seal, which connects the end frame to the turbine section. This interaction can be from vibrations or from excessive component tolerances. A means to reduce the effects of a mechanical interaction as described is to place a sacrificial wear strip in-between the contacting components. An example of the end frame of a transition duct incorporating a type of sacrificial wear strip is shown in FIG. 1. The end frame 23 contains a generally xe2x80x9cU-shapedxe2x80x9d channel 38, defined by two parallel sidewall members 24 that extend radially outward from the end frame. A typical seal between end frame 23 and turbine inlet 18 is a floating seal 40. This seal is flexible to allow for relative thermal expansion between the mating components. Under operating conditions this seal can contact the sidewalls 24 of end frame 23, causing damage to the sidewalls that requires costly repair work to the end frame region. An industry-known solution to prevent wear in this region is to place a xe2x80x9cU-shapedxe2x80x9d wear insert 42 into U-shaped channel 38, such that floating seal 40 will rub against the wear insert and not sidewalls 24. This wear insert configuration is described in detail in U.S. Pat. No. 5,749,218. Though the U-shaped wear insert has been effective it is not without its drawbacks.
The U-shaped channel 38 is approximately 0.200xe2x80x3 wide and 0.700xe2x80x3 deep, and requires an even smaller U-shaped wear insert to fit within channel 38. In order to manufacture this shape of wear insert, given the depth of channel 38, special tooling is required to form the wear insert into the U-shape cross section as well as the arc-shaped plane to match the profile of slot 38. Complicating matters of forming the wear insert is the thickness of the insert material. Given the small channel in which to install the insert and the thickness of floating seal 40, the wear insert material is extremely thin, approximately 0.018xe2x80x3, and given its U-shaped cross section, the wear insert can waver along its arc length, thereby creating a non-uniform interface to secure the wear strip to the end frame sidewalls 24.
It is an object of the present invention to provide an improved wear strip insert for an end frame of a gas turbine transition duct.
It is a further object of the present invention to provide a more cost efficient means for producing a wear strip insert for an end frame of a gas turbine transition duct, by eliminating the need for special form tooling.
The present invention addresses the manufacturing and assembly issues previously mentioned by introducing a generally xe2x80x9cL-shapexe2x80x9d wear insert design that eliminates the need for special tooling to form the insert, thereby reducing manufacturing costs. The generally L-shape design is cut from a flat sheet by typical methods, such as wire EDM, laser, or water jet cutter, in an arc length equal to the circumferential length of the U-shaped channel sidewall that the wear strip insert is covering. Intermittent tabs in the flat sheet arc length are then bent over manually to form the short leg of the desired L-shape. The preferred embodiment of the present invention will be outlined in greater detail below.
In accordance with these and other objects, which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.